Adaptive nonsingular fast integral terminal sliding mode control for servo mechanisms via variable rate cooperative reaching law

This paper investigates the unknown disturbances and actuator saturation problems of servo mechanisms. Firstly, the smooth saturation model relies on the hyperbolic tangent function to resolve the actuator saturation problem, effectively avoiding actuator failure and improving the system's service life. Secondly, the model parameter uncertainties and external disturbances in servo mechanisms are synthesized into a lumped unknown disturbance, which is then dealt with using a disturbance observer. Thirdly, an adaptive nonsingular fast integral terminal sliding mode control strategy is designed to handle the tracking control problem, which include nominal control and compensation control. Furthermore, the nominal controller introduces an improved command filter technique to handle the virtual control law, achieving stability based on the Lyapunov criterion for the entire nominal servo mechanisms. Additionally, the adaptive variable rate cooperative reaching law and the smooth function are introduced to design a compensation controller that enhances response speed and reduces or even eliminates chattering. The novel adaptive law is developed to compensate for lumped disturbance estimation errors and saturation model approximation error, while ensuring convergence and stability of closed‐loop system. Finally, the experimental results with different conditions of the permanent magnet synchronous motor servo drive system demonstrate that the proposed strategy exhibits better control performance.